1. Field of the Invention
The present invention relates to valves, and more particularly, to bore hole drill string valves for preventing the loss of drilling mud through the drill pipe during the drilling operation.
2. History of the Prior Art
In drilling oil and gas wells or the like by the rotary drilling method, the drill bit is rotated by a string of drill pipe connected to a kelly suspended in a derrick at the earth's surface. Drilling mud, or chemically laden drilling fluid, is pumped through the kelly and string of drill pipe to the drilling bit in a manner well known in the art. During the actual drilling operation, it is repeatedly necessary to disconnect the kelly from the drill string each time additional strands of drill pipe are added to the string. Since the kelly is generally filled with drilling mud or fluid, it is desirable to insert between the kelly and the drill string a valve that will allow mud to flow through the kelly and drill string during drilling, but will automatically close when the mud pumps are deactuated and the kelly is disconnected from the drill string.
The prior art is replete with valve designs for such purposes. These valves are commonly referred to as "mud saver valves" in that the drilling mud is contained rather than lost during this operation. Once disconnected, it is possible to empty the entire contents of drilling fluid in the kelly onto the drilling derrick floor. In drilling a well, it is not unusual for 100-150 barrels of drilling fluid to be lost in this manner. Such an event will result in not only a waste of large quantities of expensive drilling fluid but also the discharge of mud over the adjacent area and workmen to make the derrick floor dangerously wet and slippery. This produces a hazardous situation for personnel working on the derrick floor as well as costing time for maintenance.
Numerous prior art patents have addressed mud saver valve designs. Such valve designs generally incorporate a valve seat, a closure member and means for urging the closure member into engagement with the valve seat. For example U.S. Pat. No. 4,364,407 assigned to the inventor of the present invention discloses a valve having a tubular body connectable between the kelly and the drill string. An annular seat ring having a central opening is mounted within the body. A piston is axially movably disposed with the body for engagement within the seat ring. The piston includes a bore substantially coaxially aligned with the central opening of the seat ring and a flange extending radially outwardly from the piston to slidingly engage the interior of the body. The piston of the aforesaid patent includes a plurality of ports above the piston communicating the exterior of the piston with the bore. A plug is removably mounted in the piston above the ports to normally close the bore. The plug includes a sheer ring removably inserted in the bore and a spear axially movably mounted within the sheer ring and movable between a first position wherein the spear sealingly engages the sheer ring and a second position wherein fluid may flow upwardly between the spear and the sheer ring. A spring is provided to urge the piston into engagement with the seat ring. Other patents showing mud saver valve designs are set forth and shown in the Parker et al., U.S. Pat. No. 4,128,108; Liljestrend, U.S. Pat. No. 3,967,679; Williamson, U.S. Pat. No. 3,965,960; Litchfield et al., U.S. Pat. No. 3,738,436; Garrett, U.S. Pat. No. 3,698,411; and Taylor, U.S. Pat. No. 3,331,385.
The aforesaid patents disclose many advantages and improvements in mud saver valve designs. However, certain disadvantages exist with the prior art designs due to the very nature of the downhole environment. It is well known in the industry that the temperature, pressure and flow conditions of the borehole limit the life expectancy of drilling elements. The same holds true for mud saver valves in that the drilling mud flowing therethrough generally contains abrasive materials under pressure. Such flow can quickly disintegrate sealing surfaces. For this reason, the configuration of the sealing surface as well as the material from which the surfaces are made are integral elements of a reliable system. Moreover, axial and lateral stability of the valve itself is a key element of effective valve operation. Any misalignment in the valve seating can preclude adequate sealing which permits mud flow therefrom. Any flow of the abrasive mud will cause some deterioration in the misaligned area of the valve seat. Likewise, misalignment of mechanical parts in such high torque, high force assemblies can produce unnecessary and damaging wear upon the parts reducing their life span and requiring premature maintenance.
It would be an advantage, therefore, to overcome the disadvantages of the prior art by providing a mud flow valve having sufficient axially and lateral stability to permit effective valve seating and limited abrasive wear therethrough during high pressure mud flow conditions. The mud valve of the present invention provides such an assembly through the utilization of an elongate valve piston incorporating an exfundibular head axially aligned with an infundibular valve seat permitting the mud flow therethrough. The elongate construction reduces the potential eccentricities in valve seat alignment and the arcuate infundibular valve seating configuration facilitates the flow of abrasive mud therethrough without the deteriorating affects conventional in many prior art embodiments. Moreover, the valve seats can be constructed of suitably hard materials to withstand the aforesaid abrasive mud flow without substantial deterioration. Such an embodiment facilitates higher efficiency in operations and reduces requisite maintenance time and cost.